1. Field of the Invention
The present invention relates to a transparent electrically conductive oxide film having superior fine workability, which may be easily etched by weak acids and in which the connection resistance is decreased, and to a technique using the same.
2. Description of the Related Art
Indium-tin-oxide (ITO) films are well known as transparent electrically conductive films used for electrode circuits, pixel electrodes, and the like, in liquid crystal display devices. Since the indium-tin-oxide film which is deposited at elevated temperature and which is in the polycrystalline state has a substantially low resistance of about 200xc3x9710xe2x88x926 xcexa9xc2x7cm, it has superior low resistivity and high transmittance, which are necessary in conductors for liquid crystal display devices. ITO films have low contact resistance which may be used as the contact resistivity without any problems when tape carrier package (TCP) connection is performed. In order to form circuits and pixel electrodes by etching such indium-tin-oxide films, strong acid etchants, such as a mixed acid of HCl and HNO3, or a mixed acid of HCl and H2SO4, are required. However, if indium-tin-oxide films are etched using such strong acid etchants, the amounts of side etching will be high, resulting in difficulties in fine working.
Furthermore, as liquid crystal devices are increasingly miniaturized, as wiring in sections other than electrodes and wiring composed of indium-tin-oxide films, in which the resistance must be further decreased, wiring composed of copper is coming into use instead of wiring composed of chromium or wiring composed of tantalum as has been used.
However, the strong acid etchants used for etching indium-tin-oxide films are highly capable of etching copper wiring. Since there is a large difference in etching rate between the indium-tin-oxide films and copper and the side etching amount is also increased, if the strong acids for etching the indium-tin-oxide films are used, the copper wiring may be disconnected. Conversely, it is not possible to etch the indium-tin-oxide films using diluted hydrochloric acid or organic acids which are not likely to overetch copper wiring.
Additionally, a technique is also known in which an indium-tin-oxide film in the amorphous state is obtained by a special production method. The amorphous indium-tin-oxide can be etched by organic acids. However, the amorphous indium-tin-oxide film h as high contact resistance, which is disadvantageous.
When the indium-tin-oxide film is deposited at room temperature, a microcrystalline structure is easily produced go, and the resistance is increased to about 1,000xc3x9710xe2x88x926 xcexa9xc2x7cm, and thus, satisfactory connection resistance is not obtained.
Therefore, as transparent electrically conductive films, indium-zinc-oxide (IZO) films are receiving attention instead of indium-tin-oxide films. An indium-zinc-oxide film is known to be a superior transparent electrically conductive film suitable for fine working because an IZO film has a resistance as low as about 400xc3x9710xe2x88x926 xcexa9xc2x7cm even if deposited at room temperature. IZO films have substantially the same transmittance as that of an indium-tin-oxide film. ITO films may be etched by weak acids, and the side etching amount is small when etched by weak acids. Furthermore, if the indium-zinc-oxide film is used, for example, diluted hydrochloric acid may be selected as an etchant so as not to etch copper wiring. By using the diluted hydrochloric acid etchant, fine working can be performed even if the circuit structure in which the indium-zinc-oxide film and copper wiring are combined is employed.
However, when the indium-zinc-oxide film is used as wiring for liquid crystal devices and the wiring is used for TCP connection, the connection resistance increases, giving rise to a problem in the case when the miniaturization of wiring in liquid crystal devices is further promoted. The present inventors have also found that when the indium-zinc-oxide film is stored in air, contact resistance increases over time.
Other systems, methods, feature, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following section figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.
In view of the problems described above, it is an object of the present invention to provide a transparent electrically conductive oxide film which may be etched by weak acids in fine working, and which has low connection resistance and superior transmittance, in which resistance may be also decreased when taped carrier package (TCP) connection is performed, and resistance does not vary with time.
It is another object of the present invention to provide a target which is suitable for use in forming a transparent electrically conductive oxide film having such superior characteristics.
It is another object of the present invention to provide a method for fabricating a substrate provided with the transparent electrically conductive oxide film and to provide a liquid crystal display device provided with a substrate obtained by the fabrication method.
The resistance of an indium-zinc-oxide film may increase when TCP connection is performed. When either an indium-tin-oxide (ITO) film or an indium-zinc-oxide (IZO) film is in the amorphous state, a high-resistivity layer is formed in the surface region when left in air due to reaction with moisture, oxygen, or organic substances. The high-resistivity layer may form because a deficiency in oxygen in In2O3 (excess In) which is a source of electron carriers of the indium-zinc-oxide film is combined with moisture, oxygen, or organic substances in air, and thus the oxygen-deficiency type conductive mechanism is inhibited.
In one aspect a transparent electrically conductive oxide film is composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, and includes at least a connecting section, in which the tin content is higher than the zinc content in the connecting section, and at least the connecting section has crystallinity.
In the transparent electrically conductive oxide film composed of the compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the tin content is higher than the zinc content at least in the connecting section, and at least the connecting section has crystallinity, in addition to the conductive mechanism in which excess indium of the indium oxide produces electron carriers, the conductive mechanism in which tetravalent tin is activated to increase electron carriers by adding tin as an n-type dopant to indium functions effectively, and simultaneously, an inhibition factor of zinc which consumes electron carriers can be reduced because activated tin acts as an acceptor for electron carriers. Thus, reaction with moisture, oxygen, or organic substances in air is inhibited, and satisfactory low resistance connection is anticipated. Since the transparent electrically conductive oxide film described above can also be easily etched by weak acids and the side etching amount thereof is small, finer working of wiring is possible in comparison with an indium-tin-oxide film. Furthermore, since the transparent electrically conductive oxide film can be etched by weak acids, even if the structure provided with copper wiring is employed, it is possible to carry out etching treatment without eroding the copper wiring.
In one aspect, a transparent electrically conductive oxide film is composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of about 1 at % through about 9 at %, the atomic ratio of tin to zinc is about 1 or more, the atomic percentage of tin to the total of zinc, indium, and tin is about 20 at % or less, and at least a portion thereof has crystallinity.
By setting the contents of zinc, indium, and tin in the ranges described above, the film may be deposited in the amorphous state and then at least the connecting section thereof may be easily crystallized, satisfactory conductivity can be secured by increasing electron carriers by tin, the inhibition factor of zinc which consumes electron carriers is eliminated, and reaction with moisture, oxygen, or organic substances in air can be inhibited.
Preferably, the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of about 2 at % through about 7 at %, and the atomic-percentage of tin to the total of zinc, indium, and tin is in the range of about 5 at % through about 10 at % so that satisfactory conductivity and reaction inhibiting ability are obtained.
An electronic apparatus includes the transparent electrically conductive oxide film as at least a portion of the electric circuit thereof.
In the electronic apparatus provided with the transparent electrically conductive oxide film, even if a miniaturized wiring structure is employed, it is possible to connect the transparent electrically conductive oxide film to other components with low resistance, and even if left in air, connection resistance is not greatly deteriorated. Etching can be performed using weak acids. Thus, it is possible to provide an electronic apparatus provided with wiring which can be subjected to fine working.
Furthermore, a target is composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of 1 at % through about 12 at %, the atomic ratio of tin to zinc is about 1 or, more, and the atomic percentage of tin to the total of zinc, indium, and tin is about 22 at % or less.
If the target having the composition described above is used as a target for deposition by sputtering, even if the miniaturized wiring structure is employed, it is possible to obtain wiring of a transparent electrically conductive film in which connection to other components can be performed with low resistance, connection resistance is not greatly deteriorated if left in air, etching may be performed by weak acids, and fine working can be performed.
In the target of the present invention, preferably, the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of about 2 at % through about 10 at %, and the atomic percentage of tin to the total of zinc, indium, and tin is in the range of about 5 at % through about 12 at %.
In accordance with the present invention, a method for fabricating a substrate provided with a transparent electrically conductive oxide film includes the steps of depositing a transparent electrically conductive amorphous oxide film onto the substrate, the transparent electrically conductive amorphous oxide film being composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the atomic ratio of tin to zinc is about 1 or more; patterning the transparent electrically conductive amorphous oxide film by etching; and then performing heat treatment so that at least a portion of the transparent electrically conductive amorphous oxide film which has been patterned is crystallized.
In the transparent electrically conductive amorphous oxide film composed of the compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the tin content is higher than the zinc content at least in a connection section, and at least the connecting section has crystallinity, as the conductive mechanism of the indium-zinc-oxide, a conductive mechanism in which electron carriers are increased by activation due to the addition of tin as an n-type dopant to indium functions effectively, and simultaneously, an inhibition factor of zinc which consumes electron carriers can be reduced because activated tin acts as an acceptor for electron carriers. Thus, it is possible to provide a substrate provided with wiring in which reaction with moisture, oxygen, or organic substances in air is inhibited, and satisfactory connection is performed. Additionally, with respect to the compound oxide described above, etching can be performed by weak acids in the amorphous state when deposited, fine working is possible, and connection with low resistance can be performed after crystallization.
In accordance with the present invention, a method for fabricating a substrate provided with a transparent electrically conductive oxide film includes the steps of depositing a transparent electrically conductive amorphous oxide film onto the substrate, the transparent electrically conductive amorphous oxide film being composed of a compound oxide containing indium oxide, tin oxide, and zinc oxide, in which the atomic percentage of zinc to the total of zinc, indium, and tin is in the range of about 1 at % through about 9 at %, the atomic ratio of tin to zinc is about 1 or more, and the atomic percentage of tin to the total of zinc, indium, and tin is about 20 at % or less; patterning the transparent electrically conductive amorphous oxide film by etching; and then performing heat treatment so that at least a portion of the transparent electrically conductive amorphous oxide film which has been patterned is crystallized.
In accordance with the present invention, a liquid crystal display device includes a liquid crystal sandwiched between a pair of substrates, in which at least one of the pair of substrates comprises the substrate provided with the transparent electrically conductive oxide film described above.
It is thereby possible to provide a liquid crystal display device having the substrate provided with the transparent electrically conductive oxide film having the characteristics described above.